Pixel or image element prediction is an important part of video coding standards such as H.261, H.263, MPEG-4 and H.264 [1]. In H.264 there are three pixel prediction methods utilized, namely intra, inter and bi-prediction. Intra prediction provides a spatial predicition of the current block from previously decoded pixels of a current frame. Inter prediction gives a temporal prediction of the current block using a corresponding but displaced block in a previously decoded frame.
Multiple reference pictures may be used for inter predicition with a reference picture index to indicate which of the multiple reference pictures is used. In the P-type of inter encoding, only single directional predicition is used, and the allowable reference pictures are managed in list 0. However, in B-type of inter encoding, two lists of reference pictures are managed, list 0 and list 1. In such B-type pictures, single directional predicition using either list 0 or list 1 is allowed, or bi-predicitions using an average of a reference picture from list 0 and another reference picture from list 1.
The weighted prediction in H.264 represents a weight for respectively bi-directional predicition and also a DC offsets for the weighted combination in the slice header. The general formula for using weighting factors in inter prediction is:P=((w0*P0+w1*P1)>>Shift)+DC  (1)where P0 and w0 are the list 0 initial predictor and weighting factor and P1 and w1 are the list 1 initial predictor and weighting factor. DC represents an offset that is defined per frame basis and Shift is a shifting factor. In the case of bi-directional prediction w0=w1=0.5.
Document [2] suggests a hybrid intra-inter bi-predictive coding mode that allows both intra and inter frame predictions to be combined together for hybrid-encoding a macroblock. In this hybrid coding, an average of selected intra and inter predictions or a differently weighted combination of the intra and inter predictions is used.